Couplings are commonly used to transmit torque from one rotating body to another body. Sometimes it is desirable to incorporate axial compliance in the coupling to allow the rotating bodies to move relative to one another. In this type of coupling, the two rotating bodies are rotationally fixed and axially movable. One application for this type of coupling is a driveshaft for a motor vehicle.
U.S. Pat. No. 6,761,503 (Breese), hereby incorporated by reference in its entirety as if set forth fully herein, discloses a splined member for use in a slip joint for transmitting rotational force between two members, while accommodating a limited amount of relative axial movement therebetween. The slip joint includes a female splined member with a female tubular member and a plurality of elongated rods; a male member with a plurality of circumferentially spaced, longitudinally extending grooves; a plurality of balls disposed in the grooves; and a cage that retains the balls in a fixed relation to one another and limits the travel of the balls in the grooves. The balls engage the rods in a circumferential direction to transmit torque between the female member and the male member, while facilitating unencumbered telescopic displacement between the members.
Breese is limited in that the members are always rotationally fixed. That is, the female member and the male member cannot be disengaged from one another. Sometimes it is desirable to have a disengageable coupling, for example to change gears in a transmission. Often a combination of synchronizer rings and dog clutches are used to engage and disengage the trans-mission gears. This combination requires a considerable amount of axial space in the transmission.
U.S. Pat. No. 6,409,001 (Kerr), hereby incorporated by reference in its entirety as if set forth fully herein, discloses a multi-directional coupling including a tubular slipper, a tubular member, a race, and roller members disposed in a channel defined by the tubular slipper and the tubular member. Torque applied to the member forces the rollers to roll up the side walls of the channels, forcing the slipper to radially expand, thereby increasing the radial force exerted on the slipper against the race. As more torque is applied to the member, the slipper and the race will become rotationally locked to the member.
Kerr further includes a tapered spigot and a channel extending through the slipper and member. When the spigot is partially inserted into the channel, the coupling responds as described above. When the spigot is fully inserted into the channel, the member is prevented from rotating relative to the slipper, allowing the race to freewheel. However, Kerr is limited in that once engaged, the coupling cannot be easily disengaged while torque is applied to the member. That is, in order to reduce the radial force exerted on the slipper against the race, the slipper must rotate opposite to the member and against the torque being transmitted. Furthermore, the rollers in the Kerr design do not permit axial displacement of the tubular slipper relative to the tubular slipper.
Thus, there is a long-felt need for a disengageable coupling which permits axial displacement. There is also a long-felt need for a disengageable coupling that can be easily disengaged while transmitting torque.